As information industry rapidly has recently advanced, a variety of information processing systems, and recording methods or apparatuses suitable for those information processing systems have been developed and employed. In such recording methods, there is known ink recording using a jet for emitting ink or a plotter and thermal transfer recording using a melt type colorant or a sublimation type colorant. Apparatuses employed for the ink jet recording method are lightweight, compact-sized and noiseless and further are excellent in workability and maintainance. Moreover, the apparatuses used in those recording methods can be easily modified to enable color recording, and hence those recording methods have been widely used in recent years.
Recording methods for the ink-jet recording can be roughly classified into three methods: a method of using an aqueous dye solution of a water-soluble dye (aqueous ink), a method of using a dye solution obtained by dissolving an oil-soluble dye in an organic solvent (oily ink), and a method of using a molten solid wax containing a dye (wax ink). The method of using the aqueous ink is mainly adopted. In any of those methods, an image is formed by emitting the ink in the form of fine droplets onto a recording sheet.
The ink-jet recording method is utilized for forming an image not only on a paper sheet but also on a transparent sheet. The transparent sheet can be employed for preparing the various films such as OHP films, films for back light display, and intermediates. In more detail, the OHP films have been widely used for presentation in place of slides, the films for back light display have been widely used in place of printed posters or display boards, and the intermediates are prints which are used as a master for further reproduction. Such transparent sheet (recording sheet) usually comprises a transparent film and a colorant-receptive (absorbing) layer provided thereon. Also in the transparent sheet, an image is formed thereon as described above, so as to prepare an image of high transparency, that is, an image fixed on a clear base especially adaptable for viewing by means of transmitted light.
Further, a hard copy in which an image is formed on a sheet by the ink-jet recording method is occasionally required to have a high gloss. In more detail, the hard copy is also desired to have a high gloss appearing close to that of silver-salt photography.
An image formed on the transparent recording sheet by the ink-jet recording method is usually required to show excellent hue, saturation, and lightness. Moreover, the ink-jet recording needs a transparent recording sheet to rapidly absorb a liquid ink and to fix a liquid ink on a colorant-receptive layer (whereby ink forming the ink image is not allowed to transfer to other sheets), and further not to allow bleeding or blooming of ink, from the view-point of obtaining a clear image. The amount of ink (of ink image) unfixed on the colorant-receptive layer can be evaluated by a density of ink transferred on a white paper sheet when the paper sheet is pressed on the sheet having an ink image thereon.
The transparent recording sheet usually comprises a transparent film and a colorant-receptive layer provided thereon. The conventional colorant-receptive layer consisting mainly of resin shows a high transparency, but an amount of unfixed ink on the colorant-receptive layer is not satisfactorily reduced because the resin is apt to swell or dissolve in ink to show adhesiveness.
For example, use of a soluble or swelling substance in a colorant-receptive layer is proposed in Japanese Patent Provisional Publication No. 56(1981)-80489. Further, a great number of polymers (e.g., polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO) and carboxymethyl cellulose (CMC)) are also mentioned. The proposed colorant-receptive layer utilizes penetration effect of the aqueous ink owing to the hydrophilic group or the dissociation group of the polymer, and hence, even if the film is formed to have increased thickness, a satisfactory ink absorption speed and a satisfactory reduction of an amount of the unfixed ink cannot be obtained.
Japanese Patent Provisional Publication No. 3(1991)-104638 discloses use of crosslinked polyvinyl pyrrolidone in a colorant-receptive layer. Such a colorant-receptive layer slightly reduces an amount of the unfixed ink on the colorant-receptive layer, but it still is not satisfactory.
In order to solve those problems, various transparent sheets for forming an image of a transparency (i.e., transparent sheet having a transparent image) using inorganic particles have been proposed, such as the following:
Japanese Patent Provisional Publications No. 57(1982)-14091 and No. 61(1986)-19389 disclose a recording sheet comprising a support and a transparent layer composed of colloidal silica and water-soluble resin. The transparent layer does not has a high void volume, and therefore, the recording sheet does not give a satisfactory ink absorption speed and satisfactory reduction of an amount of the unfixed ink. Further, a recording sheet having a colorant-receptive layer having fine pores which is formed of pseudo-boehmite fine particles is described in Japanese Patent Provisional Publications No. 2(1990)-276670 and No. 3(1991)-281383. According to the studies by the inventor, however, it has been found that sufficient transparency cannot be obtained by this recording sheet because of its high refractive index of about 1.65, though the ink absorption property is satisfactorily improved and an amount of unfixed ink of the obtained ink image is satisfactorily reduced.
Japanese Patent Publication No. 61(1986)-53958 discloses a recording sheet comprising a transparent support and a transparent layer composed of synthetic silica, fine inorganic particles of refractive index of 1.44-1.55 and a water-soluble resin. The synthetic silica usually has a mean primary particle diameter of more than 10 nm, and further contains secondary particles having size of several hundreds nm. Therefore, the secondary particles are apt to scatter light applied thereto, whereby the recording sheet containing the particles can not show a satisfactory light transmittance. Further, the transparent layer has relatively large pores due to the large secondary particles and hence does not satisfactorily prevent occurrence of bleeding or blooming of ink.
Further, the following publications disclose a recording sheet having a layer of latex or polymer particle provided on a sheet.
Japanese Patent Publication No. 62(1987)-11678 discloses a sheet for ink-jet recording using a specific basic latex (polymer), which shows a satisfactory ink absorption speed and satisfactory reduction of amount of non-fixed ink of ink image. The specific basic latex is prepared by copolymerizing a monomer having a tertiary amino group or quaternary ammonium salt group, a monomer having two or more ethylenically unsaturated groups and a monomer other than these monomers. The colorant-receptive layer comprising the specific basic latex shows a satisfactory ink absorption speed and satisfactory reduction of an amount of unfixed ink on the colorant-receptive layer, but does not show a high transmittance because the particle size of the latex is large (generally approx. 0.5 .mu.m). In Example of the publication, a sheet wherein a colorant-receptive layer of the specific basic latex is formed on a paper sheet as well as a sheet wherein a colorant-receptive layer of the specific basic latex and an amount of calcium carbonate is formed on a transparent sheet, are described. Hence, the publication does not disclose a transparent recording sheet.
Japanese Patent Provisional Publication No. 5(1993)-254251 discloses a heat-sensitive recording sheet containing as a binder a micro gel, which is prepared by copolymerizing a polymerizable monomer such as alkyl (meth)acrylate or styrene and an emulsifier having at least one carbon-carbon double bond. In Example of the publication, a coating liquid containing a micro gel is coated on a paper sheet to prepare a heat-sensitive recording sheet. Hence, the publication does not disclose a transparent recording sheet, and also that for ink-jet recording. Further, in the heat-sensitive recording method, an image is formed by heating locally a recording sheet, on the other hand, in the ink-jet recording an image is formed by jetting ink onto the recording sheet. Therefore, these recording methods apparently differ from each other in the field of art.